Impact wrenches



Oct. 18, 1955 Filed Oct. 17, 1951 F. B. COOMBES IMPACT WRENCHES 2Sheets-Sheet l Oct. 18, 1955 a COQMBES 2,720,956

IMPACT WRENCHES Filed OCT 17, 1951 2 Sheets-Sheet 2 United States PatentOflfice 2,720,956 Patented Oct. 18, 1955 IMPACT WRENCHES Frank B.Coombes, Hale, England, assignor to Holman Brothers Limited, Camborne,Cornwall, England Application October 17, 1951, Serial No. 251,671

Claims. (Cl. 19230.5)

This invention relates to impact wrenches, that is devices of the classin which a succession of rotational hammer blows are imparted through ananvil to a member, such as a nut or bolt, which offers considerableresistance to rotation. More particularly, the invention relates toimpact wrenches of the kind in which a driving member, a hammer and ananvil rotate together until the resistance to the rotation of the anvilexceeds the driving torque applied to the hammer, after which the hammeris alternately disengaged from the anvil, the driving member rotatingahead of the hammer and storing energy during the disengaging movement,and re-engaged with the anvil, the stored energy imparting an angularacceleration to the hammer during the re-engaging movement so that itstrikes a blow against the anvil upon re-engagement.

In accordance with the present invention the energy for the subsequentacceleration of the hammer is stored by the compression of air or othercompressible fluid in a trapped space. This arrangement not only avoidsthe use of springs or other resilient bodies which are subject tofatigue, but also allows continuous adjustment of the magnitude of theimpacts delivered by the hammer to be effected in a very simple manner,namely by varying the initial pressure of the trapped fluid. The natureof the invention will otherwise sufficiently appear from the appendedclaims when read in the light of the following description of theparticular form of impact wrench constructed in accordance with theinvention which is shown in the accompanying drawings.

In these drawings:

Figure 1 shows a longitudinal section through the Wrench, the forwardend of the wrench being shown at the bottom of the drawing;

Figure 2 is a view similar to Figure l with the parts in difierentrelative positions;

Figures 3 and 4 show side elevations of the parts coupling together thedriving mem er and the hammer of the wrench in the relative positionswhich they occupy in Figures 1 and 2 respectively;

Figure 5 shows a ransverse section through the coupling between thehammer and anvil of the wrench;

Figures 6 and 7 are views corresponding respectively to Figures 3 and 4of a modified coupling between the driving member and the hammer.

Referring to these drawings, a casing 10 accommodates a reversiblecompressed air motor of conventional design (not shown) or othersuitable power means. The motor shaft 11 carries the run wheel 12 of anepicyclic reduction gear, the outer ring of this gear being formed on amember 13 secured between the forward end of casing it) and the rear endof a front casing 14. The planet pinions 15 of the epicyclic gear arecarried on a piston member 16, which rotatably supports the forward endof motor shaft 11 and is supported by a bearing 17 within the member 13.Rotation of shaft 11 in either direction causes rotation at a lowerspeed of the piston member 16, which constitutes thedriving member ofthe Wrench.

Projecting from the front face of the piston 16 is a spill 16a whichextends through a hammer member 18 and is rotatably supported at itsfront end in an anvil member 19. The anvil is rotatably supported by abush 20 Within the front end of the casing member 14 and its projectingfront end carries a chuck 21 shaped for engagement with the nuts orother parts which it is desired to rotate.

The hammer 18, which is axially movable Within the casing 14, is ofdouble cylindrical form, having a disc portion which is slidable uponthe spill 16a and cylindrical portions extending forwardly andrearwardly from the periphery of the disc. The rearwardly extendingcylinder engages slidably over the periphery of the piston 16, while theforwardly extending portion carries at its front end a pair of forwardlyprojecting dogs 22, adapted to engage between a pair of rearwardlyextending dogs 23 on the anvil 19 when the hammer 18 is in its forwardposition (as in Figure l) and to be withdrawn clear of the anvil dogswhen the hammer is in its rearward position (as in Figure 2).

Disposed within the front cylindrical portion of the hammer 18 are apair of annular cams, the rear cam 24 being attached by dowels 25 to thedisc portion of the hammer 18, while the front cam 26 fits upon aportion of the spill 16a which is of square or other non-circular rosssection, so that it is keyed to the spill and rotates with the drivingmember 16. This arrangement of the cams makes it a simple matter toremove and replace them if they become worn. The opposed faces of thetwo annular earns 24, 26 are each formed with two recesses of flattenedV form (see Figures 3 and 4) and each pair of opposed recesses in thetwo cams accommodates a free ball 27.

An axial bore 28 in the motor shaft 11 communicates at its rear end witha source of compressible fluid under pressure, which may conveniently bethe air supply of the motor when a compressed air motor is used. Bore 28is open at its front end to an axial bore 29 in the piston 16 and itsspill 16a. A radial bore 30 in the spill connects the axial bore to thetrapped space 31 formed between the front face of the piston 16 and therear face of the disc portion of the hammer 18. 'On the motor side ofthe radial bore 30, the bore 29 is formed with a valve seat, againstwhich a valve ball 32 is pressed by a spring 33 to close communicationbetween bore 28 and trapped space 31. Spring 33 is accommodated in bore29 and is stressed by a plug 34, screwthreaded into the front end of thespill bore. It will be appreciated that by adjusting this plug 34, whichis accessible through an axial bore in the anvil 19, the pressure of airadmitted to the trapped space 31 can be adjusted to any desired value upto that of the air supply to the motor. To minimize escape of air fromthe trapped space, seals are provided between the piston and the rearcylin drical portion of the hammer at 35, between the spill and the discportion of the hammer at 36, between the motor shaft and the piston at37 and between the adjusting plug and the spill at 38.

With the parts in their normal relative positions, as shown in Figures 1and 3, the hammer 18 is held forward by the pressure of air in thetrapped space 31, so that the free balls 27 rest in the bottoms of therecesses in the two annular earns 24, 26 and the hammer dogs 22 projectinto the spaces between the anvil dogs 23. If the chuck 21 is engagedwith a nut and the motor started, the parts remain in their normalrelative positions while the nut is being spun freely up its bolt, thedriving member 16, hammer 18 and anvil 19 rotating together. When theresistance offered by the nut exceeds a certain limiting value, theanvil and the hammer are held against rotation, but the driving membercontinues to rotate.

compressing the the trapped space;

The rotation of the front cam 26 (fast to the driving m m er) r la i eto he rear 24. st o. the ham: mer) causes the free balls 27 to roll upthe inclined faces of the recesses in the cams 24, 26, as shown in Figue and. forces the hammer rearwardl ,thereby When the hammer has movedback sufficiently for its dogs 22 to cl ar the anvil dogs 23, the hammerbegins to rotate, the dogs 22; passing over. dogs 23 as shown in Figure2. Immediately the two sets of dogs are clear of one another, the hammeris forced forward by the pressure of air in the trapped space and thehammer dogs 22 re-enter the spaces between the anvil dogs 23. Theadvance of the rear Cam 24 towards the front cam 26 causes the balls 27to roll down the, slopes of the cam recesses and accelcrates the hammerto a greater rotational speed than the drivingmember. Accordingly, whenthe hammer dogs 22 again strike the anvil dogs 23 they impart asubstantial impact to thelatter. This cycle of operations isautomatically repeated, twice during each revolution of the drivingmember. The acceleration of the hammerduring its forward movement beingdependent upon the pressure in the trapped space 31, the magnitude ofthe impacts produced can be. adjusted byaltering the setting of thescrew plug 34. l a

Therecesses in the cams 24, 26 are made of V shape, with two equal andopposite slopes, so that the wrench will operate in precisely the sameway for either direction 'of. rotation. The cam surfacesmay have aconstant slope throughout their length, or the slope may vary, so thatthe rearward movement of the hammer is at first fast and is later sloweddown. Instead of making the recesses in the two cams similar in shape,the angle of slope of one cam may be greater than that of the other.Indeed, as shown in Figures 6 and 7, one cam may be replaced by a flatthrust plate 39, all the cam action being contained in one cam 40.

Whatlclaim is: a r

:1. Anirnpact wrench of the type defined comprising a rotatable drivingmember having a'piston portion and a spilLpoflion extending forwardlyfrom the piston portion, a rotatable and reciprocable hammer having arear cylindrical portion engaging fluidtight over the piston portion ofthe driving member, a disc portion engaging fluidnight around the spillportion of the driving member and a front cylindrical portion carryingforwardly projecting dogs, a rotatable anvil coaxial withsaid drivingmember and carrying rearwardly projecting dogs adapted for engagement bysaid hammer dogs, a ball track on the forward face of said disc portionof thehammer, a second balltrack spaced forwardly from said firstball'track and secured on said spill portion of the driving member,aplurality of free balls engagedbetween said ball track,

' said driving member'being'formed-with 'a fluid inlet pas sagecommunicating with the space enclosed between the driving member and'thehammer, a non-return valve in said fluid inlet passage Spring meanstending to close said valve and means for adjusting the, pressureexerted onsaid valve by'said spring means.

2. An impact-wrench of the type defined comprising a rotatable drivingmember, a rotatable anvil coaxial'with the driving member, a hammerdisposed between the driving member and the anvil, the hammer anddriving member being arranged to enclose between them a fluidtightspace, saidhammer being-capable of reciprocating relative to'thedrivingmember and the 'anvil'to vary the volume of said space, valvemeans for admitting compressible fluid under pressure into said space,said valve 4 spill portion extending forwardly from the piston portion,a rotatable and reciprocable hammer having a rear cylindrical portionengaging fluid-tight over the piston portion of the driving member, adisc portion engaging fluid-tight around the spill portion of thedriving member and a front cylindrical portion carrying forwardlyprojecting dogs, an anvil coaxial with the driving member rotatablysupported on the forward end of said spill por tion and carryingrearwardly projecting dogs adapted for engagement by said hammer dogs,said driving member being provided with a fluid inlet passagecommunicating with a fluid-tight space enclosed between said drivingmember and said hammer, a non-return valve in said fluid inlet passage,spring means tending to close said valve, and manually and externallyoperable means for adjusting the pressure exerted on said valve by saidspring means. V

4. An impact wrench of the type defined comprising a rotatable drivingmember having a piston portion and a spill portion extending forwardlyfrom the piston portion, a rotatable and reciprocable hammer having arear cylindrical portion engaging fluid-tight over the piston portion ofthe driving member, a disc portion engaging fluid-tight around the spillportion of the driving member and a front cylindrical portion carryingforwardly projecting dogs, an anvil coaxial with the driving memberrotatably supported on the forward end of said spill por tion of thedriving member and carrying rearwardly projecting dogs adapted forengagement by said hammer dogs, said driving member being formed with anaxial bore extending throughout its length, a source of commeanspreventing fluid escaping from said space when 7 said hammer movestowards said'driving member to decrease the volume of said space,andmanually operable means for adjusting said valve means so as to varythe pressure of the fluidin said space. V

3 An i mpact wrench of the type defined comprising a rotatable drivingmember having arpiston, portion and a pressible fluid under pressurecommunicating with the rear end of said axial bore in the drivingmember, said spill portion being formed with a transverse bore connecting said axial bore of the driving member and a fluidtight spaceenclosed between said driving member and said hammer, a non-returnvalvein said axial bore be tween said radial bore and the rear end ofsaid axial bore, spring means in said axial bore forwardly of saidvalve, and plug means engaging fluid-tight in said axial bore forwardlyof said spring means and longitudinally movr able in said axial bore foradjusting the pressure exerted by said spring means on said valve, saidanvil being provided with an aperture through which said plug'means areaccessible from outside said wrench.

5. An impact wrench of the type defined comprising a rotatable drivingmember having a piston portion and a spill portion extending forwardlyfrom the piston por tion, a rotatable and reciprocable hammer having arear cylindrical portion engaging fluid-tight over the piston portion ofthe driving member, a disc portion engaging fluid-tight around the spillportion of the driving member and a front cylindrical portion carryingforwardly projecting dogs, an anvil coaxial with the driving memberrotatably supported on the forward end of said spill por tion of thedriving member and carrying rearwardly.

projecting dogs adapted for engagement by said hammer dogs, a ball trackon the forward face of said disc portion of the hammer, a second balltrack spaced forwardly from said first ball track and secured on saidspill portion of the driving member, a plurality of free' balls engagedbetween said ball tracks, said driving member being formed with an axialbore extending throughout its length, a source of compressible fluidunder pressure communi: eating with the rear end of said axial bore inthe driving member, said spill portion of the driving member beingformed with a radial bore connecting said axialbore with a fluid-tightspace enclosed between said driving member and said hammer, a non-returnball valve located in said axial bore between said radial bore and therear end of the plug is accessible from outside of said wrench forrotation thereof and consequent longitudinal movement of said plug insaid axial bore to vary the pressure exerted on said valve by saidspring whereby the pressure of the fluid in said space can be varied.

References Cited in the file of this patent UNITED STATES PATENTS ThomasAug. 30, Jimerson May 30, Worden Aug. 25, Stever Oct. 27, Thomas Jan.30,

Emery Feb. 19,

